The biggest new holdings are Kraft Foods Group and ADT. Other new holdings of interest include Spectrum Pharmaceuticals (NASDAQ: SPPI) . Spectrum has been experiencing strong growth due to the success of its colorectal cancer drug Fusilev, but that was partly due to a supply shortage faced by generic competitors. With that issue going away, Spectrum recently trimmed its growth expectations, sending the heavily shorted stock down sharply. Still, it has more than a dozen other drugs in development in its pipeline, and has broadened its scope with the recent purchase of Allos Therapeutics, which is expected to help cut costs and also includes the lymphoma drug Folotyn. Spectrum also recently secured rights for the bladder-cancer drug apaziquone.

Among holdings in which D. E. Shaw increased its stake was Acadia Pharmaceuticals (NASDAQ: ACAD) , which has tripled in value over the past year, on high hopes for its pimavanserin drug, which treats psychosis in patients with Parkinson's disease and is nearing the phase 3 trial finish line. If the drug gains FDA approval, it will enjoy little competition and could be a big winner for Acadia. The company thinks the drug also might be effective against psychosis related to Alzheimer's Disease and is conducting trials for that as well.

D. E. Shaw reduced its stake in lots of companies, including Mesabi Trust (NYSE: MSB) and Molycorp (NYSE: MCP) . With a recent hefty dividend yield of 8.2%, Mesabi Trust is a royalty trust collecting a cut of the proceeds from iron mined by a Cliffs Natural Resources subsidiary -- and then paying them out to shareholders. Unlike many companies with fixed payouts, Mesabi's fluctuate over time, along with the fortunes of the mines, and while royalty trusts often have expiration dates, Mesabi's expiration isn't happening anytime soon. A possible downside for the stock is a slowdown in demand for ore, particularly in China, which has been one of several issues for Cliffs.

Molycorp has been struggling in a tough environment and recently worried investors with a surprisingly large share offering and debt issuance. (Some worry about further capital needs, too, and don't like its negative free cash flow.) Still, for those who can accept considerable risk and volatility, there's a lot of promise in Molycorp, in part due to its acquisition of Neo Materials Technologies and its potential to become a powerful low-cost producer.

Finally, D. E. Shaw's biggest closed positions included Dollar General and enhanced common stock in Citigroup. Other closed positions of interest include VirnetX Holding (NYSEMKT: VHC) , an Internet software company with valuable patents. Some don't like that it spends a lot of time in court, but such efforts have earned it a $368 million patent-infringement victory against Apple that was recently upheld. Bulls like its potential in the growing 4G LTE market, but potential doesn't keep the lights on and the company has not been generating revenue and earnings from operations.

We should never blindly copy any investor's moves, no matter how talented the investor. But it can be useful to keep an eye on what smart folks are doing. 13-F forms can be great places to find intriguing candidates for our portfolios.

Cliffs Natural Resources has grown from a domestic iron ore producer into an international player in both the iron ore and metallurgical coal markets. It has also underwhelmed investors lately, especially after its dramatic 76% dividend cut in February. However, it could now be looked at as a possible value play due to several factors that are likely to remain advantageous for Cliffs' management. For details on these advantages and more, click here now to check out The Motley Fool's premium research report on the company.

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Selena Maranjian has been writing for the Fool since 1996 and covers basic investing and personal finance topics. She also prepares the Fool's syndicated newspaper column and has written or co-written a number of Fool books. For more financial and non-financial fare (as well as silly things), follow her on Twitter... Follow @SelenaMaranjian